I have a requirement to validate email address in a file before its send to a third party.

1. If more than basic validation is needed, then SORT is the wrong tool for this.
2. The program that write or update records in this file is the one that should validate the email address.

Escapa,
very interesting link.
I knew that "kuki1234@gmail.com" and "kuki.1234@gmail.com" are in fact the same address, and that you can use tags ("kuki1234+NEWS@gmail.com", useful if you use filters), but I thought it was specific to gmail.